In our recent studies, a novel intrakine approach was developed to effectively inactivate the chemokine coreceptor CCR-5 for the macrophage-tropic HIV-1, and SIV, with a therapeutic application for HIV-1 infection. In this study we are proposing to use a SIV model to evaluate the therapeutic potential of the novel genetic intrakine approach. The hypothesis of this proposal is that the lymphocytes from macaque monkeys can be transduced with the intrakine to inactivate CCR-5, and the transduced lymphocytes would be resistant or less susceptible to SIV infection and may have an advantage in survival and functions in SIV-infected macaques. The goals of this study are two- fold: to use the SIV model to evaluate the therapeutic potential of this genetic intrakine approach for HIV-1 therapy, and to assess virus usage of chemokine coreceptors in vivo under the selection pressure by intrakine. Specifically, we will determine the effects of intrakine expression on SIV infection and cell function in primary macaque lymphocytes in vitro. We will then evaluate the survival of the intrakine-transduced or control PBLs in SIV-infected macaques to determine whether the intrakine expression confers a survival advantage of the transduced lymphocytes in vivo. Whether the autologous administration of the intrakine-transduced lymphocytes has therapeutic benefits, such as, increasing CD4+ cell counts, decreasing virus loads will be evaluated by various assays. Growing numbers of SIV or HIV-1 co-receptors being identified imply that targeting CCR-5 might result in gaining the use of alternative co-receptors, and mutated viruses might emerge and come to predominate. Accordingly, we will serially assess the intrakine-PBL macaques or intrakine-PBL macaques at different time points postinfection. We will use the envelope complementation assay to determine the coreceptor usage of SIV in the macaques with or without the intrakine selective pressure. These experiments should be important for understanding the HIV-1 pathogenesis, and has added significance for therapy since SIV is placed under the intrakine selection pressure. In summary, the SIV model study will not only address the critical issues of the safety and therapeutic potential of the novel intrakine approach for HIV-1 gene therapy, but also may shed light on the selective forces driving the usage of the chemokine coreceptors.